Power amplifier

Abstract

A power amplifier is provided with an AD converter pulse modulating an envelope signal extracted from a high frequency modulation signal; a switching amplifier amplifying an output signal from the AD converter; a low-pass filter removing high frequency noise from an output signal from the switching amplifier; a voltage control device controlling a power supply voltage of the switching amplifier; and a high frequency amplifier amplifying a phase-modulated signal having a constant envelope and having output from the low-pass filter as a power supply. The average power of the envelope signal to be inputted to the AD converter is permitted to be constant so that an input dynamic range of the AD converter can be most efficiently used. In addition the average power of the output signal from the power amplifier is adjusted by a power supply voltage to be supplied to the switching amplifier.

1. A power amplifier amplifying a high frequency modulation signal including an amplitude modulation component and a phase-modulated component, comprising:
 an AD (Analog to Digital) converter pulse modulating an envelope signal that is the amplitude modulation component; 
 a switching amplifier amplifying an output signal from the AD converter; 
 a low-pass filter removing high frequency noise from an output signal from the switching amplifier;
 a voltage control device supplying a power supply voltage to the switching amplifier and changing the power supply voltage in accordance with a control signal from the outside; 
 
 a high frequency amplifier having an output signal from the low-pass filter as a power supply and synthesizing and outputting the output and input signals of the low-pass filter; and
 a power control device permitting an average power of an input signal to the AD converter to be constant. 
 
 
     
     
       2. The power amplifier according to  claim 1 , wherein the power control device has a gain control unit converting the average power of the input signal to the AD converter in accordance with a modulation scheme of the high frequency modulation signal. 
     
     
       3. The power amplifier according to  claim 1 , wherein an input signal to the high frequency amplifier is a phase-modulated signal having a constant envelope but not the amplitude modulation component, and
 wherein the high frequency amplifier outputs a signal obtained by multiplying the output signal from the low-pass filter by the phase-modulated signal. 
 
     
     
       4. The power amplifier according to  claim 1 , wherein an input signal to the high frequency amplifier is a high frequency modulation signal including the phase-modulated component and the amplitude modulation component. 
     
     
       5. The power amplifier according to  claim 3 , further comprising: an envelope detector extracting the envelope signal from the high frequency modulation signal; and
 a limiter extracting the phase-modulated signal from the high frequency modulation signal and outputting the extracted signal to the high frequency amplifier, 
 wherein the power control device comprises: 
 a variable gain amplifier amplifying an output signal from the envelope detector by a desired gain to be determined by a control signal from the outside and outputting the amplified signal to the AD converter; and 
 a power meter generating a control signal for setting a gain of the variable gain amplifier and a control signal for setting an output voltage from the voltage control device, based on the output signal from the envelope detector. 
 
     
     
       6. The power amplifier according to  claim 4 , further comprising an envelope detector extracting the envelope signal from the high frequency modulation signal;
 wherein the power control device comprises: 
 a variable gain amplifier amplifying an output signal from the envelope detector by a desired gain to be determined by a control signal from the outside and outputting the amplified signal to the AD converter; and 
 a power meter generating a control signal for setting a gain of the variable gain amplifier and a control signal for setting an output voltage from the voltage control device, based on the output signal from the envelope detector. 
 
     
     
       7. The power amplifier according to  claim 3 , further comprising an envelope detector extracting the envelope signal from the high frequency modulation signal; and
 a limiter extracting the phase-modulated signal from the high frequency modulation signal and outputting the extracted signal to the high frequency amplifier, 
 wherein the power control device comprises: 
 an attenuator attenuating a level of an output signal from the low-pass filter; 
 a operational amplifier having a non-inverting input terminal to which an output signal from the envelope detector is inputted and an inverting input terminal to which an output signal from the attenuator is inputted; and 
 a power meter generating a control signal for setting an output voltage from the voltage control device, based on the output signal from the envelope detector. 
 
     
     
       8. The power amplifier according to  claim 4 , further comprising an envelope detector extracting the envelope signal from the high frequency modulation signal;
 wherein the power control device comprises: 
 an attenuator attenuating a level of an output signal from the low-pass filter; 
 a operational amplifier having a non-inverting input terminal to which an output signal from the envelope detector is inputted and an inverting input terminal to which an output signal from the attenuator is inputted; and 
 a power meter generating a control signal for setting an output voltage from the voltage control device, based on the output signal from the envelope detector. 
 
     
     
       9. A power amplifier amplifying a high frequency modulation signal including an amplitude modulation component and a phase-modulated component, comprising:
 an AD converter pulse modulating an envelope signal that the amplitude modulation component; 
 a multiplier synthesizing a phase-modulated signal having a constant envelope that is the phase-modulated component and an output signal from the AD converter; 
 a high frequency amplifier amplifying an output signal from the multiplier; 
 a bandpass filter removing out-of-band noise from an output signal from the high frequency amplifier; and 
 a voltage control device supplying a power supply voltage to the high frequency amplifier and changing the power supply voltage in accordance with a control signal for controlling an average power of an output signal from the high frequency amplifier, the control signal being supplied from the outside. 
 
     
     
       10. The power amplifier according to  claim 9 , further comprising power control device permitting an average power of an input signal to the AD converter to be constant. 
     
     
       11. The power amplifier according to  claim 10 , wherein the power control device has a gain control unit converting the average power of the input signal to the AD converter in accordance with a modulation scheme of the high frequency modulation signal. 
     
     
       12. The power amplifier according to  claim 9 , further comprising: an envelope detector extracting the envelope signal from the high frequency modulation signal; and
 a limiter extracting the phase-modulated signal from the high frequency modulation signal and outputting the extracted signal to the multiplier, 
 wherein the power control device comprises: 
 a variable gain amplifier amplifying an output signal from the envelope detector by a desired gain to be determined by a control signal from the outside and outputting the amplified signal to the AD converter; and 
 a power meter generating a control signal for setting a gain of the variable gain amplifier and a control signal for setting an output voltage from the voltage control device, based on the output signal from the envelope detector. 
 
     
     
       13. The power amplifier according to  claim 9 , further comprising a first envelope detector extracting the envelope signal from the high frequency modulation signal;
 a second envelope detector extracting an envelope signal representing an envelope of an output signal from the bandpass filter; and 
 a limiter extracting the phase-modulated signal from the high frequency modulation signal and outputting the extracted signal to the multiplier, 
 wherein the power control device comprises: 
 an attenuator attenuating a level of an output signal from the second envelope detector; 
 an operational amplifier having a non-inverting input terminal to which an output signal from the first envelope detector is inputted and an inverting input terminal to which an output signal from the attenuator is inputted; and 
 a power meter generating a control signal for setting an output voltage from the voltage control device, based on the output signal from the second envelope detector. 
 
     
     
       14. A power amplifying method for amplifying a high frequency modulation signal including an amplitude modulation component and a phase-modulated component, comprising:
 pulse modulating an envelope signal that is the amplitude modulation component in an AD (Analog to Digital) converter while controlling an average power of an input signal to the AD converter to be constant; 
 amplifying an output signal from the AD converter in a switching amplifier having a power supply voltage that is changed in accordance with a control signal from the outside;
 enabling an output signal from the switching amplifier to pass through a low-pass filter, thereby removing high frequency noise; and 
 
 synthesizing an output signal from the low-pass filter and an input signal in a high frequency amplifier having the output signal from the low-pass filter as a power supply, thereby obtaining a high frequency modulation signal after the amplification, the input signal being a high frequency modulation signal including at least the amplitude modulation component. 
 
     
     
       15. A power amplifying method for amplifying a high frequency modulation signal including an amplitude modulation component and a phase-modulated component, comprising:
 pulse modulating an envelope signal that is the amplitude modulation component in an AD converter; 
 synthesizing a phase-modulated signal having a constant envelope that is the amplitude modulation component and an output signal from the AD converter with a multiplier; 
 amplifying an output signal from the multiplier in a high frequency amplifier having a power supply voltage that is changed in accordance with a control signal for controlling an average power of an output signal from the high frequency amplifier, the control signal being supplied from the outside; and 
 removing out-of-band noise from the output signal from the high frequency amplifier in a bandpass filter.